The South's lead negotiator, Pagun Amum, told AFP late Tuesday that his country is ready to resume the African Union-led talks.
Sudan withdrew from negotiations after South Sudanese troops occupied the north's main oil region of Heglig on April 10, in a conflict that led to widespread fears of all-out war.
Amum said Juba has sent a letter to the AU mediator, former South African president Thabo Mbeki, saying "we have been ready to resume talks and we are waiting."
Sudan has not reciprocated, Amum said.
"I believe it is because the government of Sudan hasn't been keen to return to talks, which is in violation of the UNSC resolution and the AU roadmap" underlying the UN resolution, he said.
The May 2 United Nations Security Council resolution gave Sudan and South Sudan two weeks -- until May 16 -- to unconditionally resume the talks.
The unanimous resolution threatened sanctions if its demands are not complied with.
It sought to avert a "serious threat to international peace and security" caused by the situation along the disputed border between the two countries, after weeks of fighting.
South Sudan's 10-day occupation of Heglig coincided with Sudanese air raids on South Sudanese territory, actions which the UN condemned.
Khartoum's foreign ministry did not respond to AFP's requests for comment about the talks, but it said late Tuesday that Mbeki would likely be in Khartoum this week "to discuss the details of negotiations, like the dates and the agenda."
Sudan's President Omar al-Bashir, an accused war criminal, said last week that Sudan "will not negotiate about any issues" unless security matters are resolved first.
An African diplomat told AFP that Khartoum does seem ready to negotiate, although "they have their own approach" by placing security first.
"They need to obviously agree on the specifics of the agenda for their discussion," he said, declining to be named.
Khartoum accuses South Sudan of backing a major insurgency in South Kordofan state, as well as in Blue Nile, and also of working with Justice and Equality Movement (JEM) rebels from Darfur.
The South says it does not back the rebels but suspected JEM fighters were seen alongside its troops during the Heglig occupation. JEM denied involvement.
South Sudan accuses the north of backing insurgents in the South as well.
The UN resolution calls on both sides to halt the practice.
Bashir is wanted by the International Criminal Court for war crimes allegedly committed in Sudan's Darfur region several years ago.
The UN resolution gave both sides two days to stop fighting. That provision has already been violated, with Sudan's army saying it fought with South Sudan along the disputed border last week while the South alleged it came under Sudanese air attack.
There has been no reported fighting along the border since then.
Khartoum's foreign ministry said it is committed to stopping hostilities but it expressed reservations about certain provisions of the UN resolution.
May 16 is also the UN's deadline for both sides to withdraw their forces from the contested Abyei region.
The South said it pulled out hundreds of its police but Sudan said it will only withdraw its troops from the Abyei area, which it seized a year ago, after a joint administrative body is established.
Abyei is among "critical" issues which the UN said must be addressed in the AU-led talks, on matters left unresolved after the South's separation last July following a 1983-2005 civil war.
These include oil payments, the status of each country's citizens resident in the other, disputed and "claimed" border areas as well as demarcation of the frontier.
South Sudan claims the Heglig area.
The South separated last July with about 75 percent of the former united Sudan's oil production, but Juba still depended on the north's pipeline and Red Sea port to export its crude.
A protracted dispute over fees for use of that infrastructure led South Sudan in January to shut its oil production after accusing the north of theft.
The Security Council gave both sides three months to conclude the talks.
A UN deadline for Sudan and South Sudan to resume talks on oil and other critical issues looked likely to pass without action on Wednesday, as South Sudan accused Khartoum of stalling.